An abr bridge with 6-32 or 4 mm threads will be fine. Just put a few drops of ultra thin super glue in the hole after thereading the posts and let it fully harden. That'll harden up the mahogany nicely and keep the posts securely in. By the way fret slots shouldn't be too tight. You can always tap the bottom of the fret tang with the edge of a chisel / file (I use a warington hammer that i've ground the sharp end to an invereted v shape)
That's a good idea with the tangs - make your own nibs on them. .023 isn't something I want to shoot for, but it's strange how much bigger the tang bumps are on the jumbo frets - to the point that the two frets would seat differently in something like a .025" groove.
After incorrectly measuring the prior saw kerf and thinking a .02" kerf was .023, I'm erring on the large side, though and will dot the edges of the frets with thin CA to make sure they stay down.
edit. I just tested both fret types in castelo box and they come out a little easy for my liking, but not on their own. A small dot of CA in three places will ensure they stay put without making them a terror to get out in ...OK, they'll never have to come out as nobody has two guitars and plays two hours a day any longer.